Heat exchange unit to regulate the temperature of recirculating hydraulic fluid for operating hydraulic systems of machinery

ABSTRACT

A heat exchange unit to maintain the temperature of an aqueous non-toxic and non-flammable hydraulic fluid supplied from a reservoir to enclosed hydraulic systems of machinery used in confined areas, such as mines and the like, within a desired temperature range.

United States Rao [ Nov. 20, 1973 HEAT EXCHANGE UNIT TO REGULATE THETEMPERATURE OF RECIRCULATING HYDRAULIC FLUm FOR OPERATING HYDRAULICSYSTEMS OF MACHINERY [75] Inventor: Prabhakar B. R. Rao, Cincinnati,

Ohio

[73] Assignee: Fluidics, 1nc., Cincinnati, Ohio [22] Filed: Mar. 2, 197221 Appl. N0.: 231,509

2,210,121 8/1940 Jewell 60/53 2,467,398 4/1949 Miller 62/243 2,511,5826/1950 Grindrod.... 62/98 2,596,195 5/1952 Arbuckle 62/435 2,888,8106/1959 Hamm 62/226 2,929,212 3/1960 Lewis 60/52 3,603,105 9/1971 Figa62/230 Primary ExaminerWil1iam J. Wye Attorney-John W. Melville et a1.

[57] ABSTRACT A heat exchange unit to maintain the temperature of anaqueous non-toxic and non-flammable hydraulic fluid supplied from areservoir to enclosed hydraulic systems of machinery used in confinedareas, such as mines and the like, within a desired temperature range.

12 Claims, 12 Drawing Figures 1 I 2024 4004 F4 mp I easzzeyo/z PATENTEI]BUY 2 0 I975 sum 2 BF 9 Pmmmuovzo 1913 3772.896

sum 3 GF 9 PATENTEBHHVPO I975 SHEET 5 CF 9 WMY PATENTEUHUY 20 1975 SHEET6 BF 9 PAIENTEUMJVPU 197s SHEET 7 EF S) PATENTEDMW 20 I915 SHEU 8 BF 9HEAT EXCHANGE UNIT TO REGULATE THE TEMPERATURE OF RECIRCULATINGHYDRAULIC FLUID FOR OPERATING HYDRAULIC SYSTEMS OF MACHINERY BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates toimprovements in heat exchangers for heat exchange between liquids, andmore particularly to a heat exchange unit to maintain the temperature ofan aqueous, non-toxic and nonflammable hydraulic fluid supplied from areservoir to enclosed hydraulic systems for machinery used in confinedplaces, such as coal mines, within a desired temperature range.

2. Description of the Prior Art 7 The operation of enclosed hydraulicsystems of machinery used in confined areas, such as coal mines and thelike, where proximity to personnel and the danger of fire and explosionmake it desirable that the hydraulic fluid be non-toxic, non-flammableand nonexplosive even if sprayed in atomized form in a confinedenclosure, have led to substantial efforts to develop a hydraulic fluidfor use in such systems which will meet these requirements.

While the prior art has long been concerned with de veloping a non-toxicand non-flammable hydraulic fluid for use in enclosed hydraulic systemsof machinery used in confined spaces, a satisfactory hydraulic fluidmeeting the aforementioned requirements has only been recentlydeveloped. Reference is hereby made specifically to a patent applicationfiled concurrently herewith in the names of James A. Peek, Peter V.Croft and Elliot H. Myers, entitled METHOD OF ACTUATING ENCLOSEDHYDRAULIC SYSTEMS AND AQUEOUS FLUID THEREFOR, application Ser. No.231,724, filed March 3, 1972, and assigned to the assignee of thepresent invention, wherein an aqueous, non-toxic, non-flammablehydraulic fluid having good dispersant, extreme pressure, lubricity,corrosioninhibiting and anti-foam properties is disclosed.

It has been found that if the aforementioned fluid is circulated throughenclosed hydraulic systems from a reservoir and returned to thereservoir, and if the temperature of the aqueous hydraulic fluidsupplied from the reservoir is regulated within the temperature range of60 85 F, the temperature of the fluid anywhere in the hydraulic systemnot exceeding about 90F, a satisfactory hydraulic fluid meeting all ofthe aforementioned requirements is obtained It will, of course, bequickly understood that the use of hydraulic fluid in an enclosedhydraulic system causes such fluid to reach an exceedingly hightemperature, in the range of 120 to 220 F, as it acts as a power fluidfor the machinery in the system. Accordingly, in order for theaforementioned hydraulic fluid to achieve satisfactory results as apower fluid in the enclosed hydraulic systems of machinery, such ascontinuous mining machines, shuttle cars and other machinery used in themining industry, it was necessary to develop a heat exchange unit whichcould carefully regulate the temperature of the hydraulic fluid. Manyprior art heat exchange units were considered, but quickly discardedbecause they were unable to maintain careful regulation of thetemperature of the hydraulic fluid over an extended period of time.Additionally, such prior art heat exchangers have many othershortcomings, in-

eluding size, inefficiency, lack of dependability under difficult miningconditions, lack of mobility and substantial dependence upon otherexternal sources in order to function. Such prior art heat exchangersare also extremely expensive, highly unreliable becuase of the failureof their electrical control components, and initial starting ofelectrically driven units tend to stall. Finally, such prior art heatexchange units are not totally explosion proof and maintenance freeunder difficult mining conditions.

SUMMARY OF THE INVENTION It is a principal object of the presentinvention to provide a heat exchange unit for carefully controlling thetemperature of an aqueous non-toxic, non-flammable, hydraulic fluid usedto actuate enclosed hydraulic systems of machinery, such as continuousmining machines, shuttle cars and other mining equipment, used inconfined places, such as coal mines, wherein the fluid is supplied froma reservoir to the enclosed hydraulic systems, circulated under pressureto the systems and returned to the reservoir for reuse, so as to preventany reaction of any of the components of the fluid with alkaline earthions and to prevent any deposit of any components at any point in thesystem.

According to the invention, the above object is achieved by a heatexchange unit which includes a hydraulic motor operable by at least aportion of the hydraulic fluid in the hydraulic system. A hydraulicmotor speed control, including a bypass circuit for hydraulic fluid notused to operate the hydraulic motor, controls the speed of the motor. Aheat exchanger is provided in communication with the bypass circuit, thehydraulic motor, and a reservoir, and receives substantially all of thehydraulic fluid from the machinery. The heat exchanger provides for heatexchange between the hydraulic fluid and a heat exchanger medium,whereby the hydraulic fluid is cooled within a desired temperature rangeand returned to the reservoir. The desired temperature range ispreferably within the range of 60 85 F, with the temperature of thehydraulic fluid anywhere in the systemnot exceeding about 90F.

A source of heat exchanger medium for the heat exchanger unit isprovided. A compressor operable by the hydraulic motor is incommunication with the heat exchanger, the compressor receiving the heatexchanger medium as it exits from the heat exchanger in vaporized form,whereby the vaporized heat exchange medium is compressed. A condenser,including fan means operable by the hydraulic motor to pull ambient airthrough and around the condenser, is in communication with thecompressor and the heat exchanger for the heat exchager medium so as toregulate the temper- .ature of the hydraulic fluid in the hydraulicsystem within the desired temperature range.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is schematic diagram showingthe heat exchange unit of the present invention as used with varioushydraulic systems which actuate the machinery involved.

FIG. 2 is a schematic diagram showing the operation of the heat exchangeunit of the present invention.

FIG. 3 is a plan view of the heat exchange unit according to the presentinvention.

FIG. 4 is a left side elevational view of the heat exchange unitaccording to the present invention.

FIG. 5 is a right side elevational view of the heat exchange unitaccording to the present invention.

FIG. 6 is a rear elevational view of the heat exchange unit according tothe present invention.

FIG. 7 is a rear elevational view of an alternate heat exchange unitaccording to the present invention.

FIG. 8 is an exploded view showing the heat exchanger of the heatexchange unit according to the present invention.

FIG. 9 is a cross sectional view taken on the line 9 9 of FIG. 5 showingthe thermostatic expansion valve.

FIG. 10 is an exploded view of the thermostatic expansion valve of FIG.9.

FIG. 11 is a cross sectional view taken on the line 11 11 of FIG. 3showing the load compensation valve.

FIG. 12 is a side elevational view, partially broken away, of the valveof FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, anenclosed hydraulic system 10 having a reservoir 12 which provides asupply of aqueous hydraulic fluid, is disclosed. The fluid is diluted tothe desired concentration either prior to introduction into thereservoir, or with suitable mixing equipment, the concentrate can beintroduced into the reservoir and sufficient water added to achieve thedesired concentration. Although the type of hydraulic fluid is not alimitation on the heat exchange unit of the present invention,preferably the hydraulic fluid utilized is in accordance with thatdisclosed in the aforementioned patent application filed concurrentlyherewith in the names of James A. Feck, Peter V. Croft and Elliot H.Myers, entitled METHOD OF ACTUATING ENCLOSED HYDRAULIC SYSTEMS AND AQUE-OUS FLUID THEREFOR, and assigned to the assignee of the presentinvention.

The hydraulic system 10 includes flexible conduits 15 and I7 and thelike leading to the various hydraulic systems which actuate themachinery involved, and therefrom return back to the reservoir 12,preferably existing on either a continuous mining machine 16, or ashuttle car 18, or any other hydraulically actuated machinery. Theflexible conduits l5 and 17 are high pressure lines leading to actuatorsand hdyraulic motors. Hydraulic fluid to the pump or the like isdirected through the intake line 19 from the reservoir 12. It will, ofcourse, be understood that a plurality of machines 16 and 18 may beconnected to a single reservoir 12 and that one or more pumps 20,including a power source in combination therewith, such as the electricmotor 22, the pumps 20 being mounted on the machines 16 and 18, as wellas gravity flow, will be utilized for circulation of the hydraulic fluidin the hydraulic system 10.

As can be seen from FIG. 1, the hydraulic fluid in the enclosed system10 is caused to pass to a heat exchange unit 24 of the present inventionhaving a capacity, for example, of up to about 35,000 B.T.U.s perhour,ifthe hydraulic system 10 includes only one machine such as acontinuous mining machine 16. However, it will, of

course, be understood that the required capacity of the heat exchangeunit 24 as well as the number of heat exchange units 24 which areincluded in the hydraulic system 10 will vary depending upon the numberof hydraulically actuated machines being operated within the system 10.

The hydraulic fluid in the hydraulic system 10 will be regulated to atemperature of F, but not exceeding F, by the heat exchange unit 24. Ingeneral, the heat exchange unit 24 will be located immediately after themachinery 16 and 18 and before the reservoir 12, in which case thehydraulic fluid is pumped therefrom to the reservoir 12.

Normally hydraulically actuated machines 16 and 18 are equipped with oneor more reservoirs. The reservoirs l2 mentioned herein will preferablybe such reservoirs. While the temperature of the fluid is caused toincrease slightly upon passing through the recirculating systems, it hasbeen found that operation in the manner disclosed in acoal mine does notresult in an increase in temperature of the hydraulic fluid above 90F.because of continuous circulation of the fluid through the hydraulicallyactuated machines 16 and 18, back to the heat exchange unit 24, and thenagain to the reservoir 12.

Introduction of fine abrasive particles into the hydraulic fluid of thehydraulic system 10 of the present invention cannot be avoided inordinary operation, but the flow of fluid can be relied upon to entrainmost of the contaminants and to carry them back to the reservoir 12where a major proportion will settle to the bottom by gravity. As shownin FIG. 2, provision can of course be made to withdraw thesecontaminants from the bottom of the reservoir 12 periodically, and thesupply conduits 14 leading to the reservoir 12 and the intake line 19 ofthe hydraulic machinery preferably are positioned intermediate the topand bottom thereof in order to avoid re-en'trainment of contaminantparticles. A magnetic chip collector 13 may also be utilized.

Referring now to FIG. 2, which discloses a schematic diagram of the heatexchange unit 24 of the present invention, as well as to the plan andelevational views of FIGS. 3 through 6, it will be seen that the heatexchange unit 24 includes a hydraulic motor 26 which is operable by atleast a portion of the hydraulic fluid in the system 10. A hydraulicmotor speed control valve 28 controls the amount of hydraulic fluidwhich is directed to the hydraulic motor 26, and thus the speed thereof.In practice, hydraulic fluid is directed through the speed control valve28 and into a high pressure line 30 leading to the motor 26. Theposition of the hydraulic line down stream of speed control valve 28 isthe priority flow line at high pressure connected to high pressure line30 going into the hydraulic motor 26. The speed control valve 28 admitsonly the specified amount of flow through the priority flow line 29 athigh pressure to the motor 26 and maintains constant speed under varyingspeed and flow conditions of the hydraulic pump 20. The hydraulic motor26 will be running at constant speed under varying conditions of heatload generated by the hydraulically actuated machinery l6 and/or 18. Theflow going through the hydraulic motor 26 is adjusted to handle acapacity of up to 35,000 B.T.U.s/hr or less depending upon the type andnumber of hydraulic machines in the system 10.

An alternate method of close temperature regulation within the desiredrange would be to either manually or automatically varying the speed ofthe hydraulic motor '26 by means of the conventional flow control valve28 shown in FIG. 2, in proportion to the heat load generated by thehydraulic equipment on a machine 16 and 18. Increasing and decreasingthe opening of the flow control valve 28 results in more or less flow tothe hydraulic motor 26, and thus more or less speed thereof and can beaccomplished by sensing thetemperature rise in the hydraulic system 10,such as at the reservoir 12.

That portion of the hydraulic fluid not directed into the high pressureline 30, as shown in FIG. 2, is directed into the bypass line 32, whichis at a lower bypass pressure and leads into the heat exchange unit 24.The portion of the hydraulic fluid not directed into the high pressureline, in the line 17, could be made to actuate subcooler 60 is aconventional cooling unit which includes an elongated chamber 62 throughwhich vapor-.

ized heat exchanger medium passes, the vaporized medium from the heatexchanger 34 entering and exiting at opposite ends 62a and 62b of thechamber 62. The condensed heat exchanger medium is cooled further as itpasses through the conduit 74A and the inlet 61A of the subcooler 60,out through the outlet 61B and into the conduit 74B. The usual finnedconduit 64 runs through the chamber 62 and provides passage forcondensed heat exchanger medium, as will be more fullyhydraulic'machinery by providing a high pressure relief valve in theline 17 before directing the line to an actuator or motor onhydrualically actuated machinery, as shown in FIG. 1. After having donethe work, the hydraulic line 17 returns at a lower pressure and isdirected into line 32, as shown in FIG. 1. As will be more fullyexplained hereinafter, the hydraulic fluid exiting from the hydraulicmotor 26 in the high pressure line 30 subsequently combines with thehydraulic fluid in the bypass line 32 prior to passing through the heatexchanger or evaporator 34, where the hydraulic fluid is cooled and thenreturned to the hydraulic system 10, such as to the reservoir 12 on themachinery 16 and 18, through the discharge line 183.

The heat exchanger 34 may be of acceptable conventional design, but ispreferably of the type disclosed in U. S. Pat. No. 2,523,990, in thename of Graham. As best seen in FIGS. 5 and 8 the heat exchanger 34includes a manifold 38 having a fluid tight cover 40. The cover 40includes therein a receiving port 42 and dis charge port 44, for thehydraulic fluid of the system 10, as well as a receiving port 46 and adischarge port 48, for the heat exchanger medium or coolant. A pluralityof conduits 50 are positioned within the manifold 38 of the heatexchanger 34. The conduits 50 have opposite extremeties 52 and 54extending through the aforementioned inlet and outlet ports 46 and 48,respectively, for the heat exchanger medium. Each conduit 50 has theportion between the center and opposite ends formed into parallel,coaxial, symetrical spirals engaged throughout the spiral portions withone another in cooperative sealing engagement throughout the length ofthe spiral portions to form a spiral passage thereabout in the manifold38. Hydraulic fluid passing through the manifold 38 surrounds the coils50 carrying the heat exchanger medium and exits through the outlet port44 leading to the discharge line 183.

It will, of course, be understood that the heat exchanger 34 providesfor heat exchange between the hydraulic fluid in the system 10 and theheat exchanger medium or refrigerant, such as FREON and the like,whereby the hydraulic fluid is cooled within the desired temperaturerange and returned to the system 10. The heat exchanger medium orrefrigerant utilized should preferably be non-toxic, non-flammable, andinert, and if possible compatible with the existing gases in the mine.

The heat exchanger medium exiting from the heat exchanger 34 proceedsthrough the heat exchanger medium outlet line 56, which may leaddirectly to the compressor 58, or to preferably a subcooler 60. The

explained hereinafter.

vaporized heat exchanger medium exiting either directly from the heatexchanger 34, or from the subcooler 60, proceeds through the conduit 56to the compressor 58, where it is compressed and exits to the condenser66. At this point, it should be noted that the hydraulic motor 26operates both the compressor 58 and the fan '78 which pulls cool ambientair through and around the condenser 66. In operation, the heat exchangeunit 24 will be utilized in underground mines where the temperatureaverages 56F. Accordingly, the cool mine air increases the efficieny ofthe heat exchange unit 24, primarily the condenser 66, and enables thecomponents thereof to be smaller and more compact. For example, the sizeof the condenser 66 may be reduced by as much as 50 percent as comparedwith condensers operating under normal conditions.

As can be seen from the drawings, the hydraulic motor 26 is positionedaxially between the condenser 66 and the fan 68, and the compressor 58.Suitable drive means 70 operatively connect the hydraulic motor 26 withthe fan 68. Additionally, a coupling unit 72 connects the hydraulicmotor 26 with the compressor 58. It should perhaps be emphasized thataligning the fan 68 with the hydraulic motor 26 and the compressor 58eliminates the requirement for a pulley drive and the like, as well asexternal cooling means for the compressor, resulting in a substantialsavings on space and cost.

Condensed heat exchanger medium from the condenser 66 proceeds through-a suitable conduit 74 (74A, 74B and 74C) either directly to the finnedconduit 64 of the subcooler 60, or if a subcooler 60 is not utilized,directly to the inlet 46 ofthe heat exchanger 34, through thethermostatic expansion valve 82.

In practice, a sight glass 76, a filter dryer 78 and a receiver ordampener 80 are positioned in the conduit 74A. The sight glass 76, whichis of conventional design, simply provides visual observation that theheat exchanger medium is properly flowing through the system. Forexample, conventional sight glasses generally include therein meanswhich may be visually actuated by the heat exchanger medium. Such meanswill be green if the medium is flowing through the system, or red if themedium is not flowing through the system.

The dryer and filter 78 is also of conventional design and simply takesmoisture, extraneous material, and acid forming materials out of theheat exchanger medium.

The receiver or dampener 80 is of the conventional type and its purposeis to cushion or dampen surges of heat exchanger medium in the heatexchange unit 24. In practice, the receiver or dampener 80 merelycomprises a hollow chamber through which the heat exchanger mediumpasses. Additionally, the receiver or dampener 80 stores excess liquidheat exchanger mediurn and aids in the servicing of the heat exchangeunit 24.

The temperature of the condensed heat exchanger medium entering the heatexchanger 34 must be regulated in order to provide satisfactory heatexchange between the hydraulic fluid and the heat exchanger medium so asto carefully regulate the temperature of the hydraulic fluid within theaforementioned desired temperature range. Briefly, this is accomplishedby a combination of a thermostatic expansion valve 82 in the line 74following the sight glass 76, the filter dryer 78, and the receiver 80,from the condenser 66 to the heat exchanger medium inlet 46 of the heatexchanger 34, and a load compensation valve 84 and associated bypasscircuit 86, joining the high pressure compressor discharge line 65between the compressor 58 and the condenser 66 with the line 74,following the thermostatic expansion valve 82.

While the means to control or regulate the temperature of the condensedheat exchanger medium entering the heat exchanger 34 may comprise onlythe thermostatic expansion valve 82, such as, for example, if the heatis constant, it has been found that best results are achieved when themeans includes a combination of a thermostatic expansion valve 82 andthe load compensation valve 84 and bypass circuit 86.

FIG. 9 discloses a cross sectional view through the thermostaticexpansion valve 82. It will first, be understood that the purpose of theexpansion valve 82 is to provide or furnish a set drop in pressure inthe condensed heat exchanger medium in line 748, prior to its reachingthe inlet port 46 of the heat exchanger 34, through line 74C. Thepurpose of such pressure drop is to control the degree of heat which theheatexchanger medium will remove from the hydraulic fluid in the heatexchanger. For example, the greater the pressure drop provided by thethermostatic expansion valve 82, the greater the quantity of heat themedium will remove from the hydraulic fluid in the heat exchanger 34. Ingeneral, the condensed heat exchanger medium in line 74B coming to thethermostatic expansion valve 82 is at a pressure of about 150 psi. Thethermostatic expansion valve 82 reduces this pressure level to about 30psi. However, the setting for the pressure dropmay be changed dependingupon the demand upon the medium.

As can be seen from FIGS. 9 and 10 the thermostatic expansion valve 82comprises a body 88 having an inlet 88a and an outlet 8811, athermostatic element, which includes a control diaphragm 92 and a remotecontrol bulb 94, including a capillary tube or suction line 95, pushrods 96, seat 98, strainer 100, pin carrier 102 carrying pin 104, spring106, including a spring guide 108, a bottom cap assembly 110, whichincludes an adjusting stem 112, and a sealed cap 114.

In operation, the push rods 96 carry the action of the diaphragm 92 tothe pin 104. Tl-le control bulb 94 is located at the outlet of the heatexchanger 34 on the suction line 56. When the control bulb 94 warms,some of the heat exchanger medium or refrigerant in the bulb vaporizesand builds up pressure in the body 88 by means of the capillary tubeconnection 95, and the diaphragm 92 moves toward the body 88. Thisforces the pin 104 to move away from the seat 98 admitting the liquidheat exchanger medium or refrigerant into the heat exchanger orevaporator 34. This action continues until the whole coil 50 within theheat exchanger 34 is cooled, and the suction line 56 begins to cool. Assoon as the suction line 56, to which the control bulb 94 is attached,becomes cooled sufficiently, the pressure in the bulb 96 decreases, dueto condensation of its refrigerant. This reduces the pressure againstthe diaphragm 92. This action causes a movement of the diaphragm 92, andthe expansion valve 82 is shut off, leaving the coil 50 of the heatexchanger 34 filled with heat exchanger medium or refrigerant vapor. Theheat exchanger 34 now lowers or decreases the low side pressure,depending upon the heat load generated by the machines 16 and 18. Whenthe heat exchange unit 24 stops, the thermostatic expansion valve 82, ifit were still open, would close because the low side pressure begins tobuild up. This clsoing action is important, because it precludes theflooding of the coil 50 in the heat exchanger 34 with liquid heatexchanger medium or refrigerant. The thermostatic expansion valve 82 isequipped with an adjustment stem 112. The adjustment stem 112 isdesigned to move the push rods 96 against the diaphragm 92. If theadjustment stem 1 12 is tunred out or counterclockwise, the push rods 96will be moved away from the diaphragm 92. This action will starve thecoil 50 of the heat exchanger 34 and result 8 in closing the pin 104before the coil 50 becomes full of liquid exchanger medium orrefrigerant. Turning the adjustment in or clockwise will increase theamount of liquid heat exchanger medium or refrigerant allowed to flowinto the coil 50 of the heat exchanger 34.

As was previously explained, the means to regulate the temperature ofthe condensed heat exchanger medium or refrigerant entering the coils 50of the heat exchanger 34 also preferably includes the load compensationvalve 84 and the bypass circuit 86, which together allow for theintroduction of compressed, vaporized heat exchanger medium orrefrigerant into the conduit 74C. Under normal conditions, the loadcompensation valve 84 is closed and vaporized heat exchanger medium isprecluded from passing through the bypass circuit 86 into the conduit74C.

The load compensation valve 84 may best be seen in FIGS. 11 and 12.Control pressure from the external equalizer connection 116 senses thepressure at the suction side in the line 56 of the compressor 58. Thispressure is transmitted through the passage 118 in the adpator 120 tothe space 122 beneath the diaphragm l24,where it exerts its pressureagainst the diaphragm range spring 126, which is held within the springbonnet 127 and against the diaphragm 124 by the cap 128. When thesuction pressure drops below the value of the spring setting for thediaphragm range spring 126, the diaphragm 124 travels downward, movingthe pilot plug 130 within the bore 132 in the adpater 120 in openingdirection with respect to the pilot port 134. This allows the pressurein the space 136 above the piston 138 in the valve body 140 to beincreased by vaporized heat exchanger medium or refrigerant flowingthrough the passage way 142 in the adapter 120. The increase in pressurewill be exerted on the piston 138 and in turn the plug spring 144, whichrests against the piston plug 146 of the bottom cap 138, opening themain port 150 and increasing the vaporized heat exchanger medium orrefrigerant flowing through it, thereby correcting for the droppingcontrol pressure sensed by the sensing means 116.

When the control pressure or suction pressure sensed by the sensingmeans 116 approaches and exceeds the 9 setting of the diaphragm rangespring 126, the diaphragm 124 is moved upward, allowing the auxiliaryplug spring 156 to move the pilot plug 130 in a closing direction withrespect to the pilot port 134. This re-' duces the amount of vaporizedheat exchanger medium or refrigerant flowing through the pilot port 134and the passage way 142. With the pilot port 134 throttled, the pressuredecreases on the top of the piston 138 in the 136, because of the bleedof the vaporized heat exchanger medium or refrigerant through theclearance around the piston 138. Accordingly, the plug spring 144 canmove the piston 138 in a closing direction, reducing the flow of thevaporized heat exchanger medium or refrigerant through the main port150, thereby correcting for the rising control pressure.

Turning now to FIGS. 3 through 6, it will be seen that the heat exchangeunit 24 is conveniently assembled within a suitable frame 152, whichincludes a base plate 154 and suitable rubber mounts 156, which dampenvibration. Suitable cowling 158 or the like may be provided surroundingthe fan 68. The hydraulic motor 26 is mounted on the base plate 154 byway of bolts 155. The shaft 27 of the motoris operable to rotate the fan68. A coupling unit 72 operably connects the other end of the shaft 27of the motor 26 with the compressor 58. The heat exchanger or evaporator34 may be mounted by way of the bracket 160 to the frame 152, as shownin FIGS. 3 through 6. However, as shown in FIG. 7, the heat exchanger orevaporator 34 may also be mounted beneath the base plate 154, adjacentthe subcooler 60, which is also mounted by way of suitable brackets 61from the base plate 154.

A vent line 162 having a valve 163 is provided in association with theheat exchanger or evaporator 34. Accordingly, when the heat exchanger orevaporator 34 is charged from a source of heat exchanger medium orrefrigerant, air in the hydraulic system may be bled from this vent lineby opening the valve 163.

The heat exchange unit 24 may be provided with suitable relief valves.For example, the compressor 58 may have a compressor relief valve 164. Ahot gas shut-off valve 166 as well as discharge and suction side servicevalves 168 and 170, respectively, may also be provided.

The heat exchange unit 24 of the present invention is also preferablyprovided with a suitable operating panel 172. This panel includes anindicator 174. This indicator, which senses the pressure in the line 56,is normally green. However, if the heat exchange unit is not functioningproperly and the suction line pressure exceeds the design pressure forthe heat exchange unit 24, the indicator will become red. Alternatively,a simple pressure gauge provided with red and green markings on thedial, both on the high and low side, could be used.

The panel also provides for the valve 163 leading to the vent line 162,as well as for a fluid thermometer 176, which registers the temperatureof the hydraulic fluid being discharged from the heat exchange unitthrough the port 178 into the hydraulic system 10. The panel 172 alsoprovides suitable connections 180 and 182 for receiving the bypass line32 and the high pressure line 30, respectively.

It has also been found desirable to include suitable vibration dampers,such as the suction vibration damper 184 and the discharge vibrationdamper 186.

While certain preferred embodiments of the invention have beenspecifically illustrated and described, it

is understood that the invention is not limited thereto, as manyvariations will be apparent to those skilled in the art, andtheinvention is to be given its broadest interpretation within the termsof the following claims.

I claim:

1. In an enclosed hydraulic system for operating hydraulic systems ofmachinery used in confined areas, such as coal mines and the like, whereproximity to personnel and the danger of fire and explosion make itdesirable that the hydraulic fluid be non-toxic and nonexplosive, of thetype which includes an aqueous hydraulic fluid, a reservoir for saidfluid, and at least one pump in connection with said reservoir and saidmachinery, the improvement, in combination therewith, which comprises aheat exchange unit to regulate the temperature of said hydraulic fluidat all times within said enclosed hydraulic system within thetemperature range of 60 F,'said heat exchange unit comprising:

1 a. a hydraulic motor operable by at least a portion of said hydraulicfluid; b. a hydraulic motor speed control, including a first bypassconduit for hydraulic fluid not used to operate said hydraulic motor;

c..a heat exchanger in communication with said first bypass, motor, andreservoir which receives substantially all of said hydraulic fluid insaid enclosed hydraulic system, said heat exchanger providing for heatexchange between said hydraulic fluid and a heat exchanger medium,whereby said hydraulic fluid is cooled within the desired temperaturerange and returned to said system;

. a source of heat exchanger medium for said heat exchange unit;

e. a compressor operable by said hydraulic motor and in communicationwith said heat exchanger, said compressor receiving said heat exchangermedium I as it exits from said heat exchanger in vaporized form, wherebysaid vaporized heat exchanger medium is compressed; I

f. a condenser including fan means operable by said motor to pullambient air through and around said condenser, said condenser being incommunication with said compressor and said heat exchanger forcondensing said compressed, vaporized heat exchanger medium; and I ,g.means to regulate the temperature of said condensed heat exchangermedium entering said heat exchanger in order to provide satisfactoryheat exchange between said hydraulic fluid and said heat exchangermedium so as to regulate the temperature of said hydraulic fluid withinsaid desired temperature range.

2. The improvement according to claim 1, wherein said heat exchangercomprises a manifold having a fluid tight cover, the cover having afirst receiving port and a first discharge port for the hydraulic fluidof the system and a second receiving port and a second discharge portfor the heat exchanger medium, and a plurality of conduits positionedwithin said manifold, said conduits having opposite extremetiesextending through said first receiving and discharge ports, each saidconduit having the portion between the center and opposite ends formedintoparallel, coaxial, symetrical spirals engaged throughout the spiralportions with one another in cooperative sealing engagement throughoutthe length of the spiral portions to form a spiral passage thereabout insaid manifold, whereby hydraulic fluid passing through said firstreceiving port into said manifold surrounds the spiral passage carryingthe heat exchanger medium and is cooled prior to exiting from saidsecond discharge port.

3. The improvement according to claim 1, wherein said hydraulic motor,condenser and compressor are in axial alignment with said motor beingpositioned between said condenser and said compressor.

4. The improvement according to claim 1, wherein a subcooler is incommunication with the outlet of said condenser and the heat exchangermedium inlet of said heat exchanger, and between the heat exchangermedium outlet of said heat exchanger and the inlet of said compressor,said subcooler comprising a chamber having a conduit therethrough, saidconduit receiving the condensed heat exchanger medium from saidcondenser and said vaporized heat exchanger medium from the heatexchanger medium outlet of said heat exchanger in said chambersurrounding said conduit, whereby condensed heat exchanger medium fromsaid condenser is further cooled prior to its entrance into said heatexchanger.

5. The improvement according to claim 1, wherein said means to regulatethe temperature of said condensed heat exchanger medium comprisescontrolling the speed of said hydraulic motor by said speed control inresponse to the temperature of said hydraulic fluid in said system.

6. The improvement according to claim 1, wherein said means to regulatethe temperature of said condensed heat exchanger medium entering saidheat exchanger comprises a thermostatic expansion valve which reducesthe pressure level of said heat exchanger medium from said condesnerprior to the introduction thereof to said heat exchanger, saidthermostatic expansion valve including means associates therewith tosense the temperature of said vaporized heat exchanger medium as itexits from said heat exchanger and to vary said reduced pressure levelin response to the temperature sensed.

7. The improvement according to calim 6, wherein said means to regulatethe temperature of said condensed heat exchanger medium also inlcudes aload compensation valve and a second bypass circuit, said second bypassjoining the vaporized heat exchanger medium discharged from saidcompressor with the flow of the heat exchanger medium through saidthermostatic expansion valve, said load compensation valve beingpositioned in said second bypass circuit and being provided with meansto sense the pressure of said vaporized heat exchanger medium at theinlet of said compressor, whereby said load compensation valve may beopened and closed, and thus the flow of compressed, vaporized heatexchanger medium through said second bypass circuit controlled, inresponse to said sensing means.

8. The improvement according to claim 3, wherein a dryer and filter ispositioned in said heat exchange unit to receive the condensed, heatexchanger medium from said condenser and to extract the moisture, acidand foreign material therefrom.

9. The improvement according to claim 1, wherein a receiver and dampenercomprising an elongated hollow chambered vessel is positioned to receivethe condensed heat exchanger medium from said condenser so as tocushion, reduce, and dampen the surges of said heat exchanger medium insaid heat exchanger unit and store excess liquid heat exchanger mediumand aids in servicing of said heat exchange unit.

10. In a method of actuating enclosed hydraulic systems of machineryused in confined spaces such as coal mines and the like, wherein anaqueous non-flammable hydraulic fluid is supplied from a reservoir tohydraulic systems, circulated through said enclosed systems underpressure, and returned to said reservoir for use, the improvement whichcomprises:

a. providing a non-toxic aqueous hydraulic fluid having a gooddispersant, extreme pressure, lubricity, corrosion inhibiting, andanti-foam properties, said fluid constituting a stable dispersion inwater; and

b. regulating the temperature of said hydraulic fluid at all timeswithin said enclosed hydraulic system within the temperature range of 60F. by the steps of:

i. lowering the pressure of said hydraulic fluid to a desired levelafter it has passed through the hydraulic systems of said machinery;

ii. passing said hydraulic fluid at a lower pressure to a heat exchangeunit;

iii. providing a heat exchanger within said heat exchange unit, saidheat exchanger having heat exchanger medium continuously passingtherethrough;

iv. directing said hydraulic fluid into heat exchange relation with saidheat exchanger medium in said heat exchanger;

v. discharging said hydraulic fluid from said heat exchanger back intosaid hydraulic system; and

vi. regulating the temperature of said heat exchanger medium enteringsaid heat exchanger in order to provide satisfactory heat exchangebetween said hydraulic fluid and said heat exchanger medium so as tocontinuously regulate the temperature of said hydraulic fluid withinsaid desired-temperature range, in response to temperature changes insaid hydraulic fluid resulting from fluctuation in heat load generatedby said hydraulic machinery.

11. The method according to claim 10, wherein the temperature of saidheat exchanger medium is regulated by sensing the temperature of saidheat exchanger medium leaving said heat exchanger and varying thereduction of the pressure level of said heat exchanger medium inresponse to the temperature sensed prior to the introduction thereofinto said heat exchanger.

12. The method according to claim 10, wherein the temperature of saidheat exchanger medium is further regulated by introducing vaporized heatexchanger medium into said heat exchanger medium following the reductionof the pressure level thereof.

1. In an enclosed hydraulic system for operating hydraulic systems ofmachinery used in confined areas, such as coal mines and the like, whereproximity to personnel and the danger of fire and explosion make itdesirable that the hydraulic fluid be nontoxic and non-explosive, of thetype which includes an aqueous hydraulic fluid, a reservoir for saidfluid, and at least one pump in connection with said reservoir and saidmachinery, the improvement, in combination therewith, which comprises aheat exchange unit to regulate the temperature of said hydraulic fluidat all times within said enclosed hydraulic system within thetemperature range of 60* - 90*F, said heat exchange unit comprising: a.a hydraulic motor operable by at least a portion of said hydraulicfluid; b. a hydraulic motor speed control, including a first bypassconduit for hydraulic fluid not used to operate said hydraulic motor; c.a heat exchanger in communication with said first bypass, motor, andreservoir which receives substantially all of said hydraulic fluid insaid enclosed hydraulic system, said heat exchanger providing for heatexchange between said hydraulic fluid and a heat exchanger medium,whereby said hydraulic fluid is cooled within the desired temperaturerange and returned to said system; d. a source of heat exchanger mediumfor said heat exchange unit; e. a compressor operable by said hydraulicmotor and in communication with said heat exchanger, said compressorreceiving said heat exchanger medium as it exits from said heatexchanger in vaporized form, whereby said vaporized heat exchangermedium is compressed; f. a condenser including fan means operable bysaid motor to pull ambient air through and around said condenser, saidcondenser being in communication with said compressor and said heatexchanger for condensing said compressed, vaporized heat exchangermedium; and g. means to regulate the temperature of said condensed heatexchanger medium entering said heat exchanger in order to providesatisfactory heat exchange between said hydraulic fluid and said heatexchanger medium so as to regulate the temperature of said hydraulicfluid within said desired temperature range.
 2. The improvementaccording to claim 1, wherein said heat exchanger comprises a manifoldhaving a fluid tight cover, the cover having a first receiving port anda first discharge port for the hydraulic fluid of the system and asecond receiving port and a second discharge port for the heat exchangermedium, and a plurality of conduits positioned within said manifold,said conduits having opposite extremeties extending through said firstreceiving and discharge ports, each said conduit having the portionbetween the center and opposite ends formed into parallel, coaxial,symetrical spirals engaged throughout the spiral portions with oneanother in cooperative sealing engagement throughout the length of thespiral portions to form a spiral passage thereabout in said manifold,whereby hydraulic fluid passing through said first receiving port intosaid manifold surrounds the spiral passage carrying the heat exchangermedium and is cooled prior to exiting from said second discharge port.3. The improvement according to claim 1, wherein said hydraulic motor,condenser and compressor are in axial alignment with said motor beingpositioned between said condenser and said compressor.
 4. Theimprovement according to claim 1, wherein a subcooler is incommunication with the outlet of said condenser and the heat exchangermedium inlet of said heat exchanger, and between the heat exchangermedium outlet of said heat exchanger and the inlet of said compressor,said subcooler comprising a chamber having a conduit therethrough, saidconduit receiving the condensed heat exchanger meDium from saidcondenser and said vaporized heat exchanger medium from the heatexchanger medium outlet of said heat exchanger in said chambersurrounding said conduit, whereby condensed heat exchanger medium fromsaid condenser is further cooled prior to its entrance into said heatexchanger.
 5. The improvement according to claim 1, wherein said meansto regulate the temperature of said condensed heat exchanger mediumcomprises controlling the speed of said hydraulic motor by said speedcontrol in response to the temperature of said hydraulic fluid in saidsystem.
 6. The improvement according to claim 1, wherein said means toregulate the temperature of said condensed heat exchanger mediumentering said heat exchanger comprises a thermostatic expansion valvewhich reduces the pressure level of said heat exchanger medium from saidcondesner prior to the introduction thereof to said heat exchanger, saidthermostatic expansion valve including means associates therewith tosense the temperature of said vaporized heat exchanger medium as itexits from said heat exchanger and to vary said reduced pressure levelin response to the temperature sensed.
 7. The improvement according tocalim 6, wherein said means to regulate the temperature of saidcondensed heat exchanger medium also inlcudes a load compensation valveand a second bypass circuit, said second bypass joining the vaporizedheat exchanger medium discharged from said compressor with the flow ofthe heat exchanger medium through said thermostatic expansion valve,said load compensation valve being positioned in said second bypasscircuit and being provided with means to sense the pressure of saidvaporized heat exchanger medium at the inlet of said compressor, wherebysaid load compensation valve may be opened and closed, and thus the flowof compressed, vaporized heat exchanger medium through said secondbypass circuit controlled, in response to said sensing means.
 8. Theimprovement according to claim 3, wherein a dryer and filter ispositioned in said heat exchange unit to receive the condensed, heatexchanger medium from said condenser and to extract the moisture, acidand foreign material therefrom.
 9. The improvement according to claim 1,wherein a receiver and dampener comprising an elongated hollow chamberedvessel is positioned to receive the condensed heat exchanger medium fromsaid condenser so as to cushion, reduce, and dampen the surges of saidheat exchanger medium in said heat exchanger unit and store excessliquid heat exchanger medium and aids in servicing of said heat exchangeunit.
 10. In a method of actuating enclosed hydraulic systems ofmachinery used in confined spaces such as coal mines and the like,wherein an aqueous non-flammable hydraulic fluid is supplied from areservoir to hydraulic systems, circulated through said enclosed systemsunder pressure, and returned to said reservoir for use, the improvementwhich comprises: a. providing a non-toxic aqueous hydraulic fluid havinga good dispersant, extreme pressure, lubricity, corrosion inhibiting,and anti-foam properties, said fluid constituting a stable dispersion inwater; and b. regulating the temperature of said hydraulic fluid at alltimes within said enclosed hydraulic system within the temperature rangeof 60* - 90*F. by the steps of: i. lowering the pressure of saidhydraulic fluid to a desired level after it has passed through thehydraulic systems of said machinery; ii. passing said hydraulic fluid ata lower pressure to a heat exchange unit; iii. providing a heatexchanger within said heat exchange unit, said heat exchanger havingheat exchanger medium continuously passing therethrough; iv. directingsaid hydraulic fluid into heat exchange relation with said heatexchanger medium in said heat exchanger; v. discharging said hydraulicfluid from said heat exchanger back into said hydraulic system; and vi.regulating the temperature of said heat exchanger mediuM entering saidheat exchanger in order to provide satisfactory heat exchange betweensaid hydraulic fluid and said heat exchanger medium so as tocontinuously regulate the temperature of said hydraulic fluid withinsaid desired temperature range, in response to temperature changes insaid hydraulic fluid resulting from fluctuation in heat load generatedby said hydraulic machinery.
 11. The method according to claim 10,wherein the temperature of said heat exchanger medium is regulated bysensing the temperature of said heat exchanger medium leaving said heatexchanger and varying the reduction of the pressure level of said heatexchanger medium in response to the temperature sensed prior to theintroduction thereof into said heat exchanger.
 12. The method accordingto claim 10, wherein the temperature of said heat exchanger medium isfurther regulated by introducing vaporized heat exchanger medium intosaid heat exchanger medium following the reduction of the pressure levelthereof.